Method of making low density paste material for battery plates



States US. Cl. 136-27 14 Claims ABSTRACT OF THE DISCLOSURE The method ofmaking battery paste for lead-acid batteries consisting of the steps:(a) mixing a slurry of lead oxide and water, including in said slurrysmall amounts of a foam producing agent and a stabilizing agent, and astrengthening material uniformly dispersed throughout; and (b)redistributing the Water in such slurry by areation with a gascontaining carbon dioxide.

This invention relates to the method of making a low density activepaste material for battery plates.

This application is a division of the application of Ernest J. Jacksonet al. Ser. No. 296,474, filed July 22, 1963, now abandoned, for Methodof Making Battery Paste and Article Produced Thereby.

For a background to this invention, reference is made to copendingapplication Ser. No. 857,566, filed Dec. 7, 1959, now United StatesLetters Patent No. 3,100,162, and assigned to the assignee of thisapplication. The method of such copending application involves two basicsteps. The first step is that of making a slurry of lead oxide and thesecond is the aeration of the slurry with a gas containing carbondioxide to thereby redistribute the water in the slurry and produce apaste of the desired characteristics of density and consistency in agreatly improved manner over prior methods.

This invention relates to a refinement of such method wherein batterypaste of extremely low density can be manufactured. Battery plates madefrom the low density paste of this invention are of a very porous naturewherein the pores lead into the interior of the plate interconnectingwith other interior pores. This network of pores provides an increasedsurface area available to the electrolyte during the discharge processresulting in greatly increased battery capacity particularly at highrates of discharge.

In the practice of this invention the slurry is made from a paste-likemixture of (1) lead oxide, (2) water, (3) a small amount of foamproducing agent, (4) a small amount of a stabilizing agent, and (5)strengthening materials thoroughly dispersed in such slurry forproviding the required mechanical strength to the resultant low densitybattery plate.

The above ingredients are thoroughly intermixed in any suitable mannersuch as by homogenizing-type mixer producing a high rate of shear toconvert the mixture to a liquid slurry. No specific procedure must befollowed in making the slurry, however, it has been found that one oftwo alternate procedures is preferable depending on the circumstances.The first such procedure is to first mix the water and the stabilizingagent along with a suitable plastic strengthening material emulsified inwater and then to add a dry powdered mixture of lead oxide and foamproducing agent to the liquid in the mixer. The second is to simply makea dry mixture of lead oxide, stabilizing agent and foam producing agentand add it to atent the water in the mixer with the emulsion of plasticstrengthening material added either before or after the dry ingredients.

Lead oxide used in making a battery paste is commercially available invarious forms. The particular type used will depend on whether apositive or negative plate is to be made and upon other variables (suchas particle size and percentage of free lead) well known to thoseskilled in the art.

Similarly, the foam producing agent and stabilizing agent selected foruse in mixing the slurry may be of various types. Such agents, ofcourse, must be compatible with each other and not form any undesirablecompounds with sulfuric acid in the finished battery. Generallyspeaking, it has been found that both anionic and non-ionic type foamproducing agents and fluorinated agents are suitable for use in theprocess. Specific examples of foam producing agents used satisfactorilyin the process are sodium lauryl sulfate, the sodium salt of analkylnaphthalene acid and fluoroalkyl phosphonate. The amount of foamproducing agent used can vary from about .013% to about 1.00% by weightof the mixture.

The stabilizing agent which serves to stabilize the slurry before it isaerated and to stabilize the paste after aeration may also be of varioustypes. Specific types which have proven satisfactory are sodiumcarboxymethylcellulose (also known as sodium cellulose glycolate) andpolyvinyl alcohol. The amount of stabilizing agent used can vary fromabout .20% to about 1.50% by weight of the mixture.

The strengthening material may also be of different types. For example,it has been found that vinyl resin plastics emulsified in water aresatisfactory. Specifically, water emulsions of polyvinyl chloride andpolyvinyl acetate provide good results. Other materials which could beused are fine wires of lead, gold, platinum, nickel, and other metalswhich remain substantially inert to the chemicals in a finished storagebattery. The purpose of the strengthening material is to provide amechanical stiffener for the finished plate to thereby maintainsufiicient rigidity in the very porous low density type plates which themethod of this invention is designed to produce. The amount of thestrengthening material used will vary from about .08% to about 1.00% byweight of the mixture depending primarily upon the type of materialused. When using water emulsions of vinyl polymers such as polyvinylchloride and polyvinyl acetate the anionic surfactant used to emulsifysuch vinyl polymers serves as th foam producing agent in the resultantlead oxide slurry.

The slurry, as prepared above, is an essentially stable product to thuspermit its storage for relatively long periods of time. The mainconsideration during storage is the evaporation of water from the slurrywhich will have an effect on the final product if such water is notreplaced. During the mixing of the slurry there are no uncontrollableand irreversible chemical reactions occurring which give off heat, etc.and cause corrosion and safety problems as is the case with priormethods using sulfuric acid as a bulking agent.

The second major step of the method is the aeration of the oxide slurrywith a suitable gas to redistribute the water in the slurry and therebyproduce a battery paste of the desired characteristics. Broadlyspeaking, this is accomplished by bringing the materials in the slurryand a suitable gas containing carbon dioxide into intimate contact witheach other. The slurry can be aerated by the use of any suitableapparatus such as by pumping the liquid slurry into a mixing chamberinto which a suitable gas is introduced under pressure by means of aplurality of jets mounted in the wall of the chamber. This can be acontinuous process wherein the material is pumped through the aeratingchamber and is mixed as it passes therethrough.

During this step the foam producing agent in the slurry serves todepress the surface tension of the water and thus facilitate theformation of gas bubbles in the paste. The stabilizing agent in theslurry serves to modify the surface of the lead oxide particles andcauses them to adhere in a uniform pattern to the gas bubbles which areformed. The result is a paste in which the water content has beenthoroughly and uniformly redistributed to provide a paste having apredetermined and accurately controlled density and consistency suitablefor application to a battery grid. By virtue of the aeration stepdescribed above a paste having improved characteristics of physicalstability is produced which will not lose its consistency uponsubsequent mechanical manipulation during application to a battery gridby suitable grid pasting machinery.

There are various gases and mixtures of gases which may be used toaerate the slurry. It has been found, however, that best results areobtained by the use of a gas containing a substantial proportion ofcarbon dioxide with any gas used in a mixture with carbon dioxide beingsubstantially inert to the slurry.

Having indicated in a general way the nature and purpose of theinvention, the following specific examples are offered as illustrativeembodiments:

EXAMPLE I The slurry was made by preparing 175 grams of a 2.00% solutionof sodium carboxymethylcellulose in water. To this solution was added:(1) grams of a water emulsion of polyvinyl chloride containing about2-6% by weight of an anionic surfactant such as sodium lauryl sulfate,and (2) 454 grams of leady litharge (containing about 25% free lead andno expanders for making positive battery plates). The slurry wasthoroughly intermixed and then aerated with carbon dioxide gas toproduce a foamed paste for application to a battery grid. The batteryplates produced by the method of this example had a density of 2.60grams/millilitre.

EXAMPLE II The slurry was made by preparing 150 grams of a 2.00%solution of sodium carboxymethylcellulose in water. To this solution wasadded: (1) 5 grams of a water emulsion of polyvinyl chloride containingabout 26% by weight of an anionic surfactant such as sodium laurylsulfate, and (2) 454 grams of leady litharge (containing about 25% freelead and no expanders for making positive battery plates). The slurrywas thoroughly intermixed and then aerated with carbon dioxide gas toproduce a foamed paste for application to a battery grid. The batteryplates produced by the method of this example had a density of 3.02grams/millilitre.

EXAMPLE III The slurry was made by preparing 290 grams of a 3.00%solution of sodium carboxymethylcellulose in water. To this solution wasadded: (1) 5 grams of a water emulsion of polyvinyl chloride containingabout 26% by weight of an anionic surfactant such as sodium laurylsulfate, and (2) 454 grams of leady litharge (containing about 25% freelead and no expanders for making positive battery plates). The slurrywas thoroughly inter mixed and then aerated with carbon dioxide gas toproduce a foamed paste for application to a battery grid. The batteryplates produced by the method of this example had a density of 1.89grams/millilitre. Such plates were tested and yielded 2.22 ampere-hourper ounce at a ampere rate at room temperature, as compared with 1.95ampere-hour per ounce for a conventional plate.

EXAMPLE IV water. To this solution was added: (1) 2.5 grams of a wateremulsion of polyvinyl acetate containing about 26% by weight of ananionic surfactant such as sodium lauryl sulfate and (2) 454 grams ofleady litharge (containing about free lead and no expanders for makingpositive battery plates). The slurry was thoroughly intermixed and thenaerated with carbon dioxide gas to produce a foamed battery paste forapplication to a battery grid. The battery plates produced by the methodof this example had a density of 2.81 grams/millilitre. Such plates weretested at -32 F. at a ampere rate and yielded 0.177 ampere-hour perounce of active material as opposed to 0.089 ampere-hour per ounce ofactive material yield from a conventional plate.

As stated previously, various gases and mixtures thereof have been usedsuccessfully in the practice of this invention. In the specific examplesoutlined above, the slurry was aerated by the introduction ofsubstantially pure carbon dioxide gas under approximately 20 p.s.i.g.through four ,6 inch diameter nozzles located in the bottom of the drumin which the slurry was mixed.

In addition to the use of substantially pure carbon dioxide as indicatedin the specific examples listed above, it has been found that variousmixtures of carbon dioxide with other gases can be employed withsatisfactory results, Specific examples of such other gases (used withcarbon dioxide) are argon, nitrogen, oxygen and air. As to the nature ofgas or gases other than carbon dioxide used in the aerating mixture, themain requirement is that such gas or gases be substantially inert to theslurry.

For best results the percentage of carbon dioxide in the mixture shouldbe over but it has been found that some foaming of the slurry isproduced by aerating with a gas containing as little as about 5% to 10%carbon dioxide. The particular percentage of carbon dioxide to be usedwill vary with a number of factors such as the desired consistency ofthe paste to be manufactured and the consistency of the slurry to befoamed. Generally speaking, it has been found that as the percentage ofcarbon dioxide in the aerating gas is increased the more thorough willbe the redistribution of Water in the paste to thereby produce a pastehaving a more sand-like and a less fluidlike consistency.

Although several embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

We claim:

1. The method of making battery paste comprising the steps of:

mixing a slurry of lead oxide and water, said slurry including smallamounts of a foam producing agen and a stabilizing agent, and astrengthening material uniformly dispersed throughout the slurry, saidslurry containing not more than about 45% water by weight; and

redistributing the water in said slurry by aeration with a gas, said gascomprising from about 10 to carbon dioxide, with any gas used in amixture with carbon dioxide being substantially inert to said slurry.

2. The method according to claim 1 wherein said strengthening materialis comprised of a plastic emulsified in water.

3. The method according to claim 2 wherein said plastic is polyvinylchloride.

4. The method according to claim 2 in which said plastic is polyvinylacetate.

5. The method according to claim 1 wherein said foam producing agent isless than about 1.00% by weight.

6. The method according to claim 1 wherein said stabilizing agent isless than 1.50% by weight.

7. The method according to claim 1 wherein said stabilizing agent issodium carboxymethylcellulose.

6 8. The method according to claim 1 wherein said stasaid strengtheningmaterial comprising about .08% to bilizing agent is polyvinyl alcohol.about 1.00% by weight of the paste.

9. The method according to claim 1 in which said gas 14. The methodaccording to claim 13 in which said comprises carbon dioxide and air.strengthening material is comprised of a vinyl resin plas- 10. Themethod according to claim 1 in which said gas 5 tie emulsified in water.comprises carbon dioxide and oxygen.

11. The method according to claim 1 in which said gas References Citedcomprises carbon dioxide and argon.

12. The method according to claim 1 in which said gas UNITED STTESPATENTS comprises carbon dioxide and nitrogen. 2,677,713 5/1954 Well at136 26 13. The method of making battery paste comprising the g 22 8:steps of:

mixing a slurry of lead oxide and water, said slurry 2,810,008 10/1957Blkerman 136125 including small amounts of a foam producing agent310601254 10/1962 Urry 7 136 24 and a stabilizing agent, and astrengthening material 3,100,162 8/1963 Sabatmo et 136*26 uniformlydispersed throughout the slurry; and FOREIGN PATENTS redistributing thewater in said slurry by aeration with a gas, said gas comprising fromabout 10% to 100% 6911861 8/1964 Canadacarbon dioxide, with any gas usedin a mixture with carbon dioxide being substantially inert to saidslurry; 0 JOHN MACK Primary Exammer said water comprising about 15% toabout 45% by A. SKAPARS, Assistant Examiner weight of the paste; saidstabilizing agent comprising about to about US. Cl. X.R.

1.50% by weight of the paste; 136--26 said foam producing agentcomprising about .013% to about 1.00% by weight of the paste;

